The invention relates to formulations and the use thereof in organically based electrochromic components.
Electrochromic displays or state indicators based on organic materials normally comprise an active electrochromic layer which, in the case of a display, is located between electrodes disposed vertically with respect to one another. Important constituents of the active layer are a redox system and a dye. The application of a voltage causes the ratio of concentrations of the redox partners with respect to one another to be shifted in the material. In this reaction, protons and/or ions in the material are liberated or bound. When a voltage is applied to the material, the shift of equilibrium of the redox partners present at the two electrodes runs in the reverse direction. This can be made visible for example via a pH-active dye.
A principle for implementing electrochromic displays is to produce the color change not by changing the pH-value in the display but to use the redox processes taking place anyway to produce a high-contrast color change by creating reductive and/or oxidative states in suitable materials. The so-called viologens and polythiophenes have become well known as material classes in this context. German Application Number DE 10 2005 032 316 (published as WO 2007/006767 and U.S. 2009/0040589) discloses polymeric 4,4′-bipyridinium structures separated from one another by an alkene spacer which are eminently suitable for this purpose. Bipyridinium salts produce a violet hue when voltage is applied. These compounds are therefore also termed viologens. This color impression results from so-called “pimerization”, a term taken to mean a stacking effect of the molecules because of their structure. If the bipyridinium salts are synthesized as polymers with long spacers, the pimerization is statistically suppressed, so that the radicals formed when voltage is applied appear blue and the reversibility of the switching process becomes more stable.
Although in general the polymeric bipyridyl derivatives of the kind used in the electrochromic formulations already have a very long service life, there is always a need to increase the service life of the formulations still further.